drivers/atm/atmtcp.c: fix error return code

Convert a zero return value on error to a negative one, as returned
elsewhere in the function.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
identifier ret; expression e1,e2;
@@
(
if (\(ret < 0\|ret != 0\))
 { ... return ret; }
|
ret = 0
)
... when != ret = e1
    when != &ret
*if(...)
{
  ... when != ret = e2
      when forall
 return ret;
}
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Acked-by: Chas Williams <chas@cmf.nrl.navy.mil>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/atm/atmtcp.c

@@ -299,6 +299,7 @@ static int atmtcp_c_send(struct atm_vcc *vcc,struct sk_buff *skb)
 	out_vcc = find_vcc(dev, ntohs(hdr->vpi), ntohs(hdr->vci));
 	read_unlock(&vcc_sklist_lock);
 	if (!out_vcc) {
+		result = -EUNATCH;
 		atomic_inc(&vcc->stats->tx_err);
 		goto done;
 	}